Geotagged environmental audio for enhanced speech recognition accuracy

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for enhancing speech recognition accuracy. In one aspect, a method includes receiving an audio signal that corresponds to an utterance recorded by a mobile device, determining a geographic location associated with the mobile device, identifying a set of geotagged audio signals that correspond to environmental audio associated with the geographic location, weighting each geotagged audio signal of the set of geotagged audio signals based on metadata associated with the respective geotagged audio signal, and using the set of weighted geotagged audio signals to perform noise compensation on the audio signal that corresponds to the utterance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/760,147, filed on Apr. 14, 2010, entitled “Geotagged EnvironmentalAudio for Enhanced Speech Recognition Accuracy,” the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND

This specification relates to speech recognition.

As used by this specification, a “search query” includes one or morequery terms that a user submits to a search engine when the userrequests the search engine to execute a search query, where a “term” ora “query term” includes one or more whole or partial words, characters,or strings of characters. Among other things, a “result” (or a “searchresult”) of the search query includes a Uniform Resource Identifier(URI) that references a resource that the search engine determines to beresponsive to the search query. The search result may include otherthings, such as a title, preview image, user rating, map or directions,description of the corresponding resource, or a snippet of text that hasbeen automatically or manually extracted from, or otherwise associatedwith, the corresponding resource.

Among other approaches, a user may enter query terms of a search queryby typing on a keyboard or, in the context of a voice query, by speakingthe query terms into a microphone of a mobile device. When submitting avoice query, the microphone of the mobile device may record ambientnoises or sounds, or “environmental audio,” in addition to spokenutterances of the user. For example, environmental audio may includebackground chatter or babble of other people situated around the user,or noises generated by nature (e.g., dogs barking) or man-made objects(e.g., office, airport, or road noise, or construction activity). Theenvironmental audio may partially obscure the voice of the user, makingit difficult for an automated speech recognition (“ASR”) engine toaccurately recognize spoken utterances.

SUMMARY

In general, one innovative aspect of the subject matter described inthis specification may be embodied in methods for adapting, training,selecting or otherwise generating, by an ASR engine, a noise model for ageographic area, and for applying this noise model to “geotagged” audiosignals (or “samples,” or “waveforms”) that are received from a mobiledevice that is located in or near this geographic area. As used by thisspecification, “geotagged” audio signals refer to signals that have beenassociated, or “tagged,” with geographical location metadata orgeospatial metadata. Among other things, the location metadata mayinclude navigational coordinates, such as latitude and longitude,altitude information, bearing or heading information, or a name or anaddress associated with the location.

In further detail, the methods include receiving geotagged audio signalsthat correspond to environmental audio recorded by multiple mobiledevices in multiple geographic locations, storing the geotagged audiosignals, and generating a noise model for a particular geographic regionusing a selected subset of the geotagged audio signals. Upon receivingan utterance recorded by a mobile device within or near the sameparticular geographic area, the ASR engine may perform noisecompensation on the audio signal using the noise model that is generatedfor the particular geographic region, and may perform speech recognitionon the noise-compensated audio signal. Notably, the noise model for theparticular geographic region may be generated before, during, or afterreceipt of the utterance.

In general, another innovative aspect of the subject matter described inthis specification may be embodied in methods that include the actionsof receiving geotagged audio signals that correspond to environmentalaudio recorded by multiple mobile devices in multiple geographiclocations, receiving an audio signal that corresponds to an utterancerecorded by a particular mobile device, determining a particulargeographic location associated with the particular mobile device,generating a noise model for the particular geographic location using asubset of the geotagged audio signals, where noise compensation isperformed on the audio signal that corresponds to the utterance usingthe noise model that has been generated for the particular geographiclocation.

Other embodiments of these aspects include corresponding systems,apparatus, and computer programs, configured to perform the actions ofthe methods, encoded on computer storage devices.

These and other embodiments may each optionally include one or more ofthe following features. In various examples, speech recognition isperformed on the utterance using the noise-compensated audio signal;generating the noise model further includes generating the noise modelbefore receiving the audio signal that corresponds to the utterance;generating the noise model further includes generating the noise modelafter receiving the audio signal that corresponds to the utterance; foreach of the geotagged audio signals, a distance between the particulargeographic location and a geographic location associated the geotaggedaudio signal is determined, and the geotagged audio signals that areassociated with geographic locations which are within a predetermineddistance of the particular geographic location, or that are associatedwith geographic locations which are among the N closest geographiclocations to the particular geographic location, are selected as thesubset of the geotagged audio signals; the geotagged audio signals thatare associated with the particular geographic location are selected asthe subset of the geotagged audio signals; the subset of the geotaggedaudio signals are selected based on the particular geographic location,and based on context data associated with the utterance; the contextdata includes data that references a time or a date when the utterancewas recorded by the mobile device, data that references a speed or anamount of motion measured by the particular mobile device when theutterance was recorded, data that references settings of the mobiledevice, or data that references a type of the mobile device; theutterance represents a voice search query, or an input to a digitaldictation application or a dialog system; determining the particulargeographic location further includes receiving data referencing theparticular geographic location from the mobile device; determining theparticular geographic location further includes determining a pastgeographic location or a default geographic location associated with thedevice; generating the noise model includes training a Gaussian MixtureModel (GMM) using the subset of the geotagged audio signals as atraining set; one or more candidate transcriptions of the utterance aregenerated, a search query is executed using the one or more candidatetranscriptions; the received geotagged audio signals are processed toexclude portions of the environmental audio that include voices of usersof the multiple mobile devices; the noise model generated for theparticular geographic location is selected from among multiple noisemodels generated for the multiple geographic locations; an areasurrounding the particular geographic location is defined, a pluralityof noise models associated with geographic locations within the area areselected from among the multiple noise models, a weighted combination ofthe selected noise models is generated, where the noise compensation isperformed using the weighted combination of selected noise models;generating the noise model further includes generating the noise modelfor the particular geographic location using the subset of the geotaggedaudio signals and using an environmental audio portion of the audiosignal that corresponds to the utterance; and/or an area is definedsurrounding the particular geographic location, and the geotagged audiosignals recorded within the area are selected as the subset of thegeotagged audio signals.

Particular embodiments of the subject matter described in thisspecification may be implemented to realize one or more of the followingadvantages. The ASR engine may provide for better noise suppression ofthe audio signal. Speech recognition accuracy may be improved. Noisemodels may be generated using environmental audio signals thataccurately reflect the actual ambient noise in a geographic area. Speechrecognition and noise model generation may be performed at the serverside, instead of on the client device, to allow for better processoptimization and to increase computational efficiency.

The details of one or more embodiments of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other potential features, aspects, and advantages ofthe subject matter will become apparent from the description, thedrawings, and the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an example system that uses geotaggedenvironmental audio to enhance speech recognition accuracy.

FIG. 2 is a flow chart of an example of a process.

FIG. 3 is a flow chart of another example of a process.

FIG. 4 is a swim lane diagram of an example of a process.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a diagram of an example system 100 that uses geotaggedenvironmental audio to enhance speech recognition accuracy. FIG. 1 alsoillustrates a flow of data within the system 100 during states (a) to(i), as well as a user interface 158 that is displayed on a mobiledevice 104 during state (i).

In more detail, the system 100 includes a server 106 and an ASR engine108, which are in communication with mobile client communicationdevices, including mobile devices 102 and the mobile device 104, overone or more networks 110. The server 106 may be a search engine, adictation engine, a dialogue system, or any other engine or system thatuses transcribed speech. The networks 110 may include a wirelesscellular network, a wireless local area network (WLAN) or Wi-Fi network,a Third Generation (3G) or Fourth Generation (4G) mobiletelecommunications network, a private network such as an intranet, apublic network such as the Internet, or any appropriate combinationthereof.

The states (a) through (i) depict a flow of data that occurs when anexample process is performed by the system 100. The states (a) to (i)may be time-sequenced states, or they may occur in a sequence that isdifferent than the illustrated sequence.

Briefly, according the example process illustrated in FIG. 1, the ASRengine 108 receives geotagged, environmental audio signals 130 from themobile devices 102 and generates geo-specific noise models 112 formultiple geographic locations. When an audio signal 138 that correspondsto an utterance recorded by the mobile device 104 is received, aparticular geographic location associated with the mobile device 104 (orthe user of the mobile device 104) is determined. The ASR engine 108transcribes the utterance using the geo-specific noise model thatmatches, or that is otherwise suitable for, the particular geographiclocation, and one or more candidate transcriptions 146 are communicatedfrom the ASR engine 108 to the server 106. Where the server 106 is asearch engine, the server 106 executes one or more search queries usingthe candidate transcriptions 146, generates search results 152, andcommunicates the search results 152 to the mobile device 104 fordisplay.

In more detail, during state (a), the mobile devices 102 communicategeotagged audio signals 130 that include environmental audio (referredto by this specification as “environmental audio signals”) to the ASRengine 108 over the networks 110. In general, environmental audio mayinclude any ambient sounds that occur (naturally or otherwise) at aparticular location. Environmental audio typically excludes the sounds,utterances, or voice of the user of the mobile device.

The device 102 a communicates an audio signal 130 a that has been taggedwith metadata 132 a that references “Location A,” the device 102 bcommunicates an audio signal 130 b that has been tagged with metadata132 b that references “Location B,” and the device 102 c communicates anaudio signal 130 c that has been tagged with metadata 132 c that alsoreferences “Location B.” The metadata 132 may be associated with theaudio signals 130 by mobile devices 102, as illustrated, or the metadatamay be associated with the audio signals 130 by the ASR engine 108 or byanother server after inferring a location of a mobile device 102 (or ofthe user of the mobile device 102).

The environmental audio signals 130 may each include a two-second (ormore) snippet of relatively high quality audio, such as sixteenkilohertz lossless audio signals. The environmental audio signals 130may be associated with metadata that references the geographic locationof the respective mobile device 102 when the environmental audio wasrecorded, captured or otherwise obtained.

The environmental audio signals 130 may be manually uploaded from themobile devices 102 to the ASR engine 108. For instance, environmentalaudio signals 130 may be generated and communicated in conjunction withthe generation and communication of images to a public image database orrepository. Alternatively, for users who opt to participate,environmental audio signals 130 may be automatically obtained andcommunicated from the mobile devices 102 to the ASR engine 108 withoutrequiring an explicit, user actuation before each environmental audiosignal is communicated to the ASR engine 108.

The metadata 132 may describe locations in any number of differentformats or levels of detail or granularity. For example, the metadata132 a may include a latitude and longitude associated with thethen-present location of the mobile device 102 a, and the metadata 132 cmay include an address or geographic region associated with thethen-present location of the mobile device 102 c. Furthermore, since themobile device 102 b is illustrated as being in a moving vehicle, themetadata 132 b may describe a path of the vehicle (e.g., including astart point and an end point, and motion data). Additionally, themetadata 132 may describe locations in terms of location type (e.g.,“moving vehicle,” “on a beach,” “in a restaurant,” “in tall building,”“South Asia,” “rural area,” “someplace with construction noise,”“amusement park,” “on a boat,” “indoors,” “underground,” “on a street,”“forest”). A single audio signal may be associated with metadata thatdescribes one or more locations.

The geographic location associated with the audio signal 138 may insteadbe described in terms of a bounded area, expressed as a set ofcoordinates that define the bounded area. Alternatively, the geographiclocation may be defined using a region identifier, such as a state nameor identifier, city name, idiomatic name (e.g., “Central Park”), acountry name, or the identifier of arbitrarily defined region (e.g.,“cell/region ABC123”).

Before associating a location with the environmental audio signal, themobile devices 102 or the ASR engine 108 may process the metadata toadjust the level of detail of the location information (e.g., todetermine a state associated with a particular set of coordinates), orthe location information may be discretized (e.g., by selecting aspecific point along the path, or a region associated with the path).The level of detail of the metadata may also be adjusted by specifyingor adding location type metadata, for example by adding an “on thebeach” tag to an environmental audio signal whose associated geographiccoordinates are associated with a beach location, or by adding a“someplace with lots of people” tag to an environmental audio signalthat includes the sounds of multiple people talking in the background.

During state (b), the ASR engine 108 receives the geotaggedenvironmental audio signals 130 from the mobile devices 102, and storesthe geotagged audio signals (or portions thereof) in the collection 114of environmental audio signals, in the data store 111. As describedbelow, the collection is used for training, adapting, or otherwisegenerating one or more geographic location-specific (or “geo-specific”)noise models 112.

Because environmental audio signals in the collection 114 should notinclude users' voices, the ASR engine 108 may use a voice activitydetector to verify that the collection 114 of environmental audiosignals only includes audio signals 130 that correspond to ambientnoise, or to filter out or otherwise identify or exclude audio signals130 (or portions of the audio signals 130) that include voices of thevarious users of the mobile devices 102.

The collection 114 of the ambient audio signals stored by the ASR engine108 may include hundreds, thousands, millions, or hundreds of millionsof environmental audio signals. In the illustrated example, a portion orall of the geo-tagged environmental audio signal 130 a may be stored inthe collection 114 as the environmental audio signal 124, a portion orall of the geo-tagged environmental audio signal 130 b may be stored inthe collection 114 as the environmental audio signal 126 a, and aportion or all of the geotagged environmental audio signal 130 c may bestored in the collection 114 as the environmental audio signal 120 b.

Storing an environmental audio signal 130 in the collection may includedetermining whether a user's voice is encoded in the audio signal 130,and determining to store or determining not to store the environmentalaudio signal 130 in the collection based on determining that the user'svoice is or is not encoded in the audio signal 130, respectively.Alternatively, storing an environmental audio signal in the collectionmay include identifying a portion of the environmental audio signal 130that includes the user's voice, altering the environmental audio signal130 by removing the portion that includes the user's voice or byassociating metadata which references the portion that includes theuser's voice, and storing the altered environmental audio signal 130 inthe collection.

Other context data or metadata associated with the environmental audiosignals 130 may be stored in the collection 114 as well. For example,the environmental audio signals included in the collection 114 can, insome implementations, include other metadata tags, such as tags thatindicate whether background voices (e.g., cafeteria chatter) are presentwithin the environmental audio, tags that identify the date on which aparticular environmental audio signal was obtained (e.g., used todetermine a sample age), or tags that identify whether a particularenvironmental audio signal deviates in some way from other environmentalaudio signals of the collection that were obtained in the same orsimilar location. In this manner, the collection 114 of environmentalaudio signals may optionally be filtered to exclude particularenvironmental audio signals that satisfy or that do not satisfyparticular criteria, such as to exclude particular environmental audiosignals that are older than a certain age, or that include backgroundchatter that may identify an individual or otherwise be proprietary orprivate in nature.

In an additional example, data referencing whether the environmentalaudio signals of the collection 114 were manually or automaticallyuploaded may be tagged in metadata associated with the environmentalaudio signals. For example, some of the noise models 112 may begenerated using only those environmental audio signals that wereautomatically uploaded, or that were manually uploaded, or differentweightings may be assigned to each category of upload during thegenerating of the noise models.

Although the environmental audio signals of the collection 114 have beendescribed as including an explicit tag that identifies a respectivegeographic location, in other implementations, such as where theassociation between an audio signal and a geographic location may bederived, the explicit use of a tag is not required. For example, ageographic location may be implicitly associated with an environmentalaudio signal by processing search logs (e.g., stored with the server106) to determine geographic location information for a particularenvironmental audio signal. Accordingly, receipt of a geo-taggedenvironmental audio signals by the ASR engine 108 may include obtainingan environmental audio signal that does not expressly include a geo-tag,and deriving and associating one or more geo-tags for the environmentalaudio signal.

During state (c), an audio signal 138 is communicated from the mobiledevice 104 to the ASR engine 108 over the networks 110. Although themobile device 102 is illustrated as being different a different devicethan the mobile devices 104, in other implementations the audio signal138 is communicated from one of the mobile devices 104 that provided angeo-tagged environmental audio signal 130.

The audio signal 138 includes an utterance 140 (“Gym New York”) recordedby the mobile device 104 (e.g., when the user implicitly or explicitlyinitiates a voice search query). The audio signal 138 includes metadata139 that references the geographic location “Location B.” In addition toincluding the utterance 140, the audio signal 138 may also include asnippet of environmental audio, such as a two second snippet ofenvironmental audio that was recorded before or after the utterance 140was spoken. While the utterance 140 is described an illustrated in FIG.1 as a voice query, in other example implementations the utterance maybe an voice input to dictation system or to a dialog system.

The geographic location (“Location B”) associated with the audio signal138 may be defined using a same or different level of detail as thegeographic locations associated with the environmental audio signalsincluded in the collection 114. For example, the geographic locationsassociated with the environmental audio signals included in thecollection 114 may correspond to geographic regions, while thegeographic location associated with the audio signal 138 may correspondto a particular geographic coordinate. Where the level of detail isdifferent, the ASR engine 108 may process the geographic metadata 139 orthe metadata associated with the environmental audio signals of thecollection 114 to align the level of detail, so that a subset selectionprocess can be performed.

The metadata 139 may be associated with the audio signal 138 by themobile device 104 (or the user of the mobile device 104) based onlocation information that is current when the utterance 140 is recorded,and may be communicated with the audio signal 138 from the mobile device104 to the ASR engine 108. Alternatively, the metadata may be associatedwith the audio signal 138 by the ASR engine 108, based on a geographiclocation that the ASR engine 108 infers for the mobile device 104 (orthe user of the mobile device 104).

The ASR engine 108 may infer the geographic location using the user'scalendar schedule, user preferences (e.g., as stored in a user accountof the ASR engine 108 or the server 106, or as communicated from themobile device 104), a default location, a past location (e.g., the mostrecent location calculated by a GPS module of the mobile device 104),information explicitly provided by the user when submitting the voicesearch query, from the utterances 104 themselves, triangulation (e.g.,WiFi or cell tower triangulation), a GPS module in the mobile device104, or dead reckoning. The metadata 139 may include accuracyinformation that specifies an accuracy of the geographic locationdetermination, signifying a likelihood that the mobile device 104 wasactually in the particular geographic location specified by the metadata139 at the time when the utterance 140 was recorded.

Other metadata may also be included with the audio signal 138. Forexample, metadata included with the audio signals may include a locationor locale associated with the respective mobile device 102. For example,the locale information may describe, among other selectable parameters,a region in which the mobile device 102 is registered, or the languageor dialect of the user of the mobile device 102. The speech recognitionmodule 118 may use this information to select, train, adapt, orotherwise generate noise, speech, acoustic, popularity, or other modelsthat match the context of the mobile device 104.

In state (d), the ASR engine 108 selects a subset of the environmentalaudio signals in the collection 114, and uses a noise model generatingmodule 116 to train, adapt, or otherwise generate one or more noisemodels 112 (e.g., Gaussian Mixture Models (GMMs)) using the subset ofthe environmental audio signals, for example by using the subset of theenvironmental audio signals as a training set for the noise model. Thesubset may include all, or fewer than all of the environmental audiosignals in the collection 114.

In general, the noise models 112, along with speech models, acousticmodels, popularity models, and/or other models, are applied to the audiosignal 138 to translate or transcribe the spoken utterance 140 into oneor more textual, candidate transcriptions 146, and to generate speechrecognition confidence scores to the candidate transcriptions. The noisemodels, in particular, are used for noise suppression or noisecompensation, to enhance the intelligibility of the spoken utterance 140to the ASR engine 108.

In more detail, the noise model generating module 116 may generate anoise model 120 b for the geographic location (“Location B”) associatedwith the audio signal 138 using the collection 114 of audio signals,specifically the environmental audio signals 126 a and 126 b that weregeotagged as having been recorded at or near that geographic location,or at a same or similar type of location. Since the audio signal 138 isassociated with this geographic location (“Location B”), theenvironmental audio included in the audio signal 138 itself may be usedto generate a noise model for that geographic location, in addition toor instead of the environmental audio signals 126 a and 126 b.Similarly, the noise model generating module 116 may generate a noisemodel 120 a for another geographic location (“Location A”), using theenvironmental audio signal 124 that was geotagged as having beenrecorded at or near that other geographic location, or at a same orsimilar type of location. If the noise model generating module 116 isconfigured to select environmental audio signal that were geotagged ashaving been recorded near the geographic location associated with theaudio signal 138, and if “Location A” is near “Location B,” the noisemodel generating module 116 may generate a noise model 120 b for“Location B” also using the environmental audio signal 124.

In addition to the geotagged location, other context data associatedwith the environmental audio signals of the collection 114 may be usedto select the subset of the environmental audio signals to use togenerate the noise models 112, or to adjust a weight or effect that aparticular audio signal is to have upon the generation . For example,the ASR engine 108 may select a subset of the environmental audiosignals in the collection 114 whose contextual information indicatesthat they are longer than or shorter than a predetermined period oftime, or that they satisfy certain quality or recency criteria.Furthermore, the ASR engine 108 may select, as the subset, environmentalaudio signals in the collection 114 whose contextual informationindicates that they were recorded using a mobile device that has asimilar audio subsystem as the mobile device 104.

Other context data which may be used to select the subset of theenvironmental audio signals from the collection 114 may include, in someexamples, the time information, date information, data referencing aspeed or an amount of motion measured by the particular mobile deviceduring recording, other device sensor data, device state data (e.g.,Bluetooth headset, speaker phone, or traditional input method), a useridentifier if the user opts to provide one, or information identifyingthe type or model of mobile device. The context data, for example, mayprovide an indication of conditions surrounding the recording of theaudio signal 138.

In one example, context data supplied with the audio signal 138 by themobile device 104 may indicate that the mobile device 104 is travelingat highway speeds along a path associated with a highway. The ASR 108may infer that the audio signal 138 was recorded within a vehicle, andmay select a subset of the environmental audio signals in the collection114 that are associated with an “inside moving vehicle” location type.In another example, context data supplied with the audio signal 138 bythe mobile device 104 may indicate that the mobile device 104 is in arural area, and that the utterance 140 was recorded on a Sunday at 6:00am. Based on this context data, the ASR 108 may infer that it accuracyof the speech recognition would not be improved if the subset includedenvironmental audio signals that were recorded in urban areas duringrush hour. Accordingly, the context data may be used by the noise modelgenerating module 116 to filter the collection 114 of environmentalaudio signals when generating noise models 112, or by the speechrecognition module 118 to select an appropriate noise model 112 for aparticular utterance.

In some implementations, the noise model generating module 116 mayselect a weighted combination of the environmental audio signals of thecollection 114 based upon the proximity of the geographic locationsassociated with the audio signals to the geographic location associatedwith the audio signal 138. The noise model generating module 116 mayalso generate the noise models 112 using environmental audio included inthe audio signal 138 itself, for example environmental audio recordedbefore or after the utterances were spoken, or during pauses betweenutterances.

For instance, the noise model generating module 116 can first determinethe quality of the environmental audio signals stored in the collection114 relative to the quality of the environmental audio included in theaudio signal 138, and can choose to generate a noise model using theaudio signals stored in the collection 114 only, using the environmentalaudio included in the audio signal 138 only, or any appropriate weightedor unweighted combination thereof. For instance, the noise modelgenerating module 116 may determine that the audio signal 138 includesan insignificant amount of environmental audio, or that high qualityenvironmental audio is stored for that particular geographic location inthe collection 114, and may choose to generate the noise model withoutusing (or giving little weight to) the environmental audio included inthe audio signal 138.

In some implementations, the noise model generating module 116 selects,as the subset, the environmental audio signals from the collection 114that are associated with the N (e.g., five, twenty, or fifty) closestgeographic locations to the geographic location associated with theaudio signal 138. When the geographic location associated with the audiosignal 138 describes a point or a place (e.g., coordinates), a geometricshape (e.g., a circle or square) may be defined relative to that thatgeographic location, and the noise model generating module 116 mayselect, as the subset, audio signals from the collection 114 that areassociated with geographic regions that are wholly or partially locatedwithin the defined geometric shape.

If the geographic location associated with the audio signal 138 has beendefined in terms of a location type (i.e., “on the beach,” “city”), andASR engine 108 may select environmental audio signals that areassociated with a same or a similar location type, even if the physicalgeographic locations associated with the selected audio signals are notphysically near the geographic location associated with the audio signal138. For instance, a noise model for an audio signal that was recordedon the beach in Florida may be tagged with “on the beach” metadata, andthe noise model generating module 116 may select, as the subset,environmental audio signals from the collection 114 whose associatedmetadata indicate that they were also recorded on beaches, despite thefact that they were recorded on beaches in Australia, Hawaii, or inIceland.

The noise model generating module 116 may revert to selecting the subsetbased on matching location types, instead of matching actual, physicalgeographic locations, if the geographic location associated with theaudio signal 138 does not match (or does not have a high quality match)with any physical geographic location associated with an environmentalaudio signal of the collection 114. Other matching processes, such asclustering algorithms, may be used to match audio signals withenvironmental audio signals.

In addition to generating general, geo-specific noise models 112, thenoise model generating module 116 may generate geo-specific noise modelsthat are targeted or specific to other criteria as well, such asgeo-specific noise models that are specific to different device types ortimes of day. A targeted sub-model may be generated based upon detectingthat a threshold criterion has been satisfied, such as determining thata threshold number of environmental audio signals of the collection 114refer to the same geographic location, and share another same or similarcontext (e.g., time of day, day of the week, motion characteristics,device type, etc.).

The noise models 112 may be generated before, during, or after theutterance 140 has been received. For example, multiple environmentalaudio signals, incoming from a same or similar location as the utterance140, may be processed in parallel with the processing of the utterance,and may be used to generate noise models 112 in real time or near realtime, to better approximate the live noise conditions surrounding themobile device 104.

In state (e), the speech recognition module 118 of the ASR engine 108performs noise compensation on the audio signal 138 using thegeo-specific noise model 120 b for the geographic location associatedwith the audio signal 138, to enhance the accuracy of the speechrecognition, and subsequently performs the speech recognition on thenoise-compensated audio signal. When the audio signal 138 includesmetadata that describes a device type of the mobile device 104, the ASRengine 108 may apply a noise model 122 that is specific to both thegeographic location associated with the audio signal, and to the devicetype of the mobile device 104. The speech recognition module 118 maygenerate one or more candidate transcriptions 146 that match theutterance encoded in the audio signal 138, and speech recognitionconfidence values for the candidate transcriptions.

During state (f), one or more of the candidate transcriptions 146generated by the speech recognition module 118 are communicated from theASR engine 108 to the server 106. Where the server 106 is a searchengine, the candidate transcriptions may be used as candidate queryterms, to execute one or more search queries. The ASR engine 108 mayrank the candidate transcriptions 146 by their respective speechrecognition confidence scores before transmitting them to the server106. By transcribing spoken utterances and providing candidatetranscriptions to the server 106, the ASR engine 108 may provide a voicesearch query capability, a dictation capability, or a dialogue systemcapability to the mobile device 104.

The server 106 may execute one or more search queries using thecandidate query terms, generates a file 152 that references searchresults 160. The server 106, in some examples, may include a web searchengine used to find references within the Internet, a phone book typesearch engine used to find businesses or individuals, or anotherspecialized search engine (e.g., a search engine that providesreferences to entertainment listings such as restaurants and movietheater information, medical and pharmaceutical information, etc.).

During state (h), the server 106 provides the file 152 that referencesthe search results 160 to the mobile device 104. The file 152 may be amarkup language file, such as an eXtensible Markup Language (XML) orHyperText Markup Language (HTML) file.

During state (i), the mobile device 104 displays the search results 160on a user interface 158. Specifically, the user interface includes asearch box 157 that displays the candidate query term with the highestspeech recognition confidence score (“Gym New York”), an alternate queryterm suggestion region 159 that displays another of the candidate queryterm that may have been intended by the utterance 140 (“Jim Newark”), asearch result 160 a that includes a link to a resource for “New YorkFitness” 160 a, and a search result 160 b that includes a link to aresource for “Manhattan Body Building” 160 b. The search result 160 amay further include a phone number link that, when selected, may bedialed by the mobile device 104.

FIG. 2 is a flowchart of an example of a process 200. Briefly, theprocess 200 includes receiving one or more geotagged environmental audiosignals, receiving an utterance associated with a geographic location,and generating a noise model based in part upon the geographic location.Noise compensation may be performed on the audio signal, with the noisemodel contributing to improving an the accuracy of speech recognition.

In more detail, when process 200 begins, a geotagged audio signalcorresponding to environmental audio is received (202). The geotaggedaudio signal may be recorded by a mobile device in a particulargeographic location. The geotagged audio signal may include associatedcontext data such as a time, date, speed, or amount of motion measuredduring the recording of the geotagged audio signal or a type of devicewhich recorded the geotagged audio signal. The received geotagged audiosignal may be processed to exclude portions of the environmental audiothat include a voice of a user of the mobile device. Multiple geotaggedaudio signals recorded in one or more geographic locations may bereceived and stored.

An utterance recorded by a particular mobile device is received (204).The utterance may include a voice search query, or may be an input to adictation or dialog application or system. The utterance may includeassociated context data such as a time, date, speed, or amount of motionmeasured during the recording of the geotagged audio signal or a type ofdevice which recorded the geotagged audio signal.

A particular geographic location associated with the mobile device isdetermined (206). For example, data referencing the particulargeographic location may be received from the mobile device, or a pastgeographic location or a default geographic location associated with themobile device may be determined.

A noise model is generated for the particular geographic location usinga subset of geotagged audio signals (208). The subset of geotagged audiosignals may be selected by determining, for each of the geotagged audiosignals, a distance between the particular geographic location and ageographic location associated the geotagged audio signal; and selectingthose geotagged audio signals which are within a predetermined distanceof the particular geographic location, or that are associated withgeographic locations which are among the N closest geographic locationsto the particular geographic location.

The subset of geotagged audio signals may be selected by identifying thegeotagged audio signals associated with the particular geographiclocation, and/or by identifying the geotagged audio signals that areacoustically similar to the utterance. The subset of geotagged audiosignals may be selected based both on the particular geographic locationand on context data associated with the utterance.

Generating the noise model may include training a GMM using the subsetof geotagged audio signals as a training set. Some noise reduction orseparation algorithms, such as non-negative matrix factorization (NMF),can use the feature vectors themselves, not averages that arerepresented by the Gaussian components. Other algorithms, such asAlgonquin, can use either GMMs or the feature vectors themselves, withartificial variances.

Noise compensation is performed on the audio signal that corresponds tothe utterance, using the noise model that has been generated for theparticular geographic location, to enhance the audio signal or otherwisetake decrease the uncertainty of the utterance due to noise (210).

Speech recognition is performed on the noise-compensated audio signal(212). Performing the speech recognition may include generating one ormore candidate transcriptions of the utterance. A search query may beexecuted using the one or more candidate transcriptions, or one or moreof the candidate transcriptions can be provided as an output of adigital dictation application. Alternatively, one or more of thecandidate transcriptions may be provided as an input to a dialog system,to allow a computer system to converse with the user of the particularmobile device.

FIG. 3 is a flowchart of an example of a process 300. Briefly, theprocess 300 includes collecting geotagged audio signals and generatingmultiple noise models based, in part, upon particular geographiclocations associated with each of the geotagged audio signals. One ormore of these noise models may be selected when performing speechrecognition upon an utterance based, in part, upon a geographic locationassociated with the utterance.

In more detail, when process 300 begins, a geotagged audio signalcorresponding to environmental audio is received (302). The geotaggedaudio signal may be recorded by a mobile device in a particulargeographic location. The received geotagged audio signal may beprocessed to exclude portions of the environmental audio that includethe voice of the user of the mobile device. Multiple geotagged audiosignals recorded in one or more geographic locations may be received andstored.

Optionally, context data associated with the geotagged audio signal isreceived (304). The geotagged audio signal may include associatedcontext data such as a time, date, speed, or amount of motion measuredduring the recording of the geotagged audio signal or a type of devicewhich recorded the geotagged audio signal.

One or more noise models are generated (306). Each noise model may begenerated for a particular geographic location or, optionally, alocation type, using a subset of geotagged audio signals. The subset ofgeotagged audio signals may be selected by determining, for each of thegeotagged audio signals, a distance between the particular geographiclocation and a geographic location associated the geotagged audio signaland selecting those geotagged audio signals which are within apredetermined distance of the particular geographic location, or thatare associated with geographic locations which are among the N closestgeographic locations to the particular geographic location. The subsetof geotagged audio signals may be selected by identifying the geotaggedaudio signals associated with the particular geographic location. Thesubset of geotagged audio signals may be selected based both on theparticular geographic location and on context data associated with thegeotagged audio signals. Generating the noise model may include traininga Gaussian Mixture Model (GMM) using the subset of geotagged audiosignals.

An utterance recorded by a particular mobile device is received (308).The utterance may include a voice search query. The utterance mayinclude associated context data such as a time, date, speed, or amountof motion measured during the recording of the geotagged audio signal ora type of device which recorded the geotagged audio signal.

A geographic location is detected (310). For example, data referencingthe particular geographic location may be received from a GPS module ofthe mobile device.

A noise model is selected (312). The noise model may be selected fromamong multiple noise models generated for multiple geographic locations.Context data may optionally contribute to selection of a particularnoise model among multiple noise models for the particular geographiclocation.

Speech recognition is performed on the utterance using the selectednoise model (314). Performing the speech recognition may includegenerating one or more candidate transcriptions of the utterance. Asearch query may be executed using the one or more candidatetranscriptions.

FIG. 4 shows a swim lane diagram of an example of a process 400 forenhancing speech recognition accuracy using geotagged environmentalaudio. The process 400 may be implemented by a mobile device 402, an ASRengine 404, and a search engine 406. The mobile device 402 may provideaudio signals, such as environmental audio signals or audio signals thatcorrespond to an utterance, to the ASR engine 404. Although only onemobile device 402 is illustrated, the mobile device 402 may represent alarge quantity of mobile devices 402 contributing environmental audiosignals and voice queries to the process 400. The ASR engine 404 maygenerate noise models based upon the environmental audio signals, andmay apply one or more noise models to an incoming voice search querywhen performing speech recognition. The ASR engine 404 may providetranscriptions of utterances within a voice search query to the searchengine 406 to complete the voice search query request.

The process 400 begins with the mobile device 402 providing 408 ageotagged audio signal to the ASR engine 404. The audio signal mayinclude environmental audio along with an indication regarding thelocation at which the environmental audio was recorded. Optionally, thegeotagged audio signal may include context data, for example in the formof metadata. The ASR engine 404 may store the geotagged audio signal inan environmental audio data store.

The mobile device 402 provides 410 an utterance to the ASR engine 404.The utterance, for example, may include a voice search query. Therecording of the utterance may optionally include a sample ofenvironmental audio, for example recorded briefly before or after therecording of the utterance.

The mobile device 402 provides 412 a geographic location to the ASRengine 404. The mobile device, in some examples, may providenavigational coordinates detected using a GPS module, a most recent (butnot necessarily concurrent with recording) GPS reading, a defaultlocation, a location derived from the utterance previously provided, ora location estimated through dead reckoning or triangulation oftransmission towers. The mobile device 402 may optionally providecontext data, such as sensor data, device model identification, ordevice settings, to the ASR engine 404.

The ASR engine 404 generates 414 a noise model. The noise model may begenerated, in part, by training a GMM. The noise model may be generatedbased upon the geographic location provided by the mobile device 402.For example, geotagged audio signals submitted from a location at ornear the location of the mobile device 402 may contribute to a noisemodel. Optionally, context data provided by the mobile device 402 may beused to filter geotagged audio signals to select those most appropriateto the conditions in which the utterances were recorded. For example,the geotagged audio signals near the geographic location provided by themobile device 402 may be filtered by a day of the week or a time of day.If a sample of environmental audio was included with the utteranceprovided by the mobile device 402, the environmental audio sample mayoptionally be included in the noise model.

The ASR engine 404 performs speech recognition 416 upon the providedutterance. Using the noise model generated by the ASR engine 404, theutterance provided by the mobile device 402 may be transcribed into oneor more sets of query terms.

The ASR engine 404 forwards 418 the generated transcription(s) to thesearch engine 406. If the ASR engine 404 generated more than onetranscription, the transcriptions may optionally be ranked in order ofconfidence. The ASR engine 404 may optionally provide context data tothe search engine 406, such as the geographic location, which the searchengine 406 may use to filter or rank search results.

The search engine 406 performs 420 a search operation using thetranscription(s). The search engine 406 may locate one or more URIsrelated to the transcription term(s).

The search engine 406 provides 422 search query results to the mobiledevice 402. For example, the search engine 406 may forward HTML codewhich generates a visual listing of the URI(s) located.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. For example, various formsof the flows shown above may be used, with steps re-ordered, added, orremoved. Accordingly, other implementations are within the scope of thefollowing claims.

Embodiments and all of the functional operations described in thisspecification may be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. Embodiments may be implemented asone or more computer program products, i.e., one or more modules ofcomputer program instructions encoded on a computer readable medium forexecution by, or to control the operation of, data processing apparatus.The computer readable medium may be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus may include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) may be written in any form of programminglanguage, including compiled or interpreted languages, and it may bedeployed in any form, including as a stand alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program may be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programmay be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification may beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows may also be performedby, and apparatus may also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Moreover, a computer may be embedded inanother device, e.g., a tablet computer, a mobile telephone, a personaldigital assistant (PDA), a mobile audio player, a Global PositioningSystem (GPS) receiver, to name just a few. Computer readable mediasuitable for storing computer program instructions and data include allforms of non volatile memory, media and memory devices, including by wayof example semiconductor memory devices, e.g., EPROM, EEPROM, and flashmemory devices; magnetic disks, e.g., internal hard disks or removabledisks; magneto optical disks; and CD ROM and DVD-ROM disks. Theprocessor and the memory may be supplemented by, or incorporated in,special purpose logic circuitry.

To provide for interaction with a user, embodiments may be implementedon a computer having a display device, e.g., a CRT (cathode ray tube) orLCD (liquid crystal display) monitor, for displaying information to theuser and a keyboard and a pointing device, e.g., a mouse or a trackball,by which the user may provide input to the computer. Other kinds ofdevices may be used to provide for interaction with a user as well; forexample, feedback provided to the user may be any form of sensoryfeedback, e.g., visual feedback, auditory feedback, or tactile feedback;and input from the user may be received in any form, including acoustic,speech, or tactile input.

Embodiments may be implemented in a computing system that includes aback end component, e.g., as a data server, or that includes amiddleware component, e.g., an application server, or that includes afront end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user may interact with animplementation, or any combination of one or more such back end,middleware, or front end components. The components of the system may beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude a local area network (“LAN”) and a wide area network (“WAN”),e.g., the Internet.

The computing system may include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the disclosure or of what maybe claimed, but rather as descriptions of features specific toparticular embodiments. Certain features that are described in thisspecification in the context of separate embodiments may also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment mayalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination may in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments, and it should beunderstood that the described program components and systems maygenerally be integrated together in a single software product orpackaged into multiple software products.

In each instance where an HTML file is mentioned, other file types orformats may be substituted. For instance, an HTML file may be replacedby an XML, JSON, plain text, or other types of files. Moreover, where atable or hash table is mentioned, other data structures (such asspreadsheets, relational databases, or structured files) may be used.

Thus, particular embodiments have been described. Other embodiments arewithin the scope of the following claims. For example, the actionsrecited in the claims may be performed in a different order and stillachieve desirable results.

1. A system comprising: one or more computers; and a computer-readablemedium coupled to the one or more computers having instructions storedthereon which, when executed by the one or more computers, cause the oneor more computers to perform operations comprising: receiving an audiosignal that corresponds to an utterance recorded by a mobile device;determining a geographic location associated with the mobile device;identifying a set of geotagged audio signals that correspond toenvironmental audio associated with the geographic location; weightingeach geotagged audio signal of the set of geotagged audio signals basedon metadata associated with the respective geotagged audio signal; andusing the set of weighted geotagged audio signals to perform noisecompensation on the audio signal that corresponds to the utterance. 2.The system of claim 1, wherein the operations further comprise receivinggeotagged audio signals, each geotagged audio signal including themetadata associated with the respective geotagged audio signal.
 3. Thesystem of claim 1, wherein the operations further comprise: receivinggeotagged audio signals; generating the metadata for each geotaggedaudio signal; and associating the metadata with the respective geotaggedaudio signal.
 4. The system of claim 1, wherein weighting each geotaggedaudio signal comprises weighting each geotagged audio signal of the setof geotagged audio signals based on the metadata associated with therespective geotagged audio signal and metadata associated with the audiosignal that corresponds to an utterance.
 5. The system of claim 1,wherein the metadata indicates whether background voices are present inthe respective geotagged audio signal, and weighting each geotaggedaudio signal comprises weighting each geotagged audio signal based onwhether background voices are present in the respective geotagged audiosignal.
 6. The system of claim 1, wherein the metadata indicates anaccuracy of geographic location information associated with therespective geotagged audio signal, and weighting each geotagged audiosignal comprises weighting each geotagged audio signal based on theaccuracy of the geographic location information associated with therespective geotagged audio signal.
 7. The system of claim 1, wherein themetadata indicates a length of the respective geotagged audio signal,and weighting each geotagged audio signal comprises weighting eachgeotagged audio signal based on the length of the respective geotaggedaudio signal.
 8. The system of claim 1, wherein the metadata indicates aquality of the respective geotagged audio signal, and weighting eachgeotagged audio signal comprises weighting each geotagged audio signalbased on the quality of the respective geotagged audio signal.
 9. Thesystem of claim 1, wherein the metadata indicates a geographic locationassociated with the respective geotagged audio signal, and weightingeach geotagged audio signal comprises weighting each geotagged audiosignal based on proximity of the geographic location associated with therespective geotagged audio signal to the geographic location associatedwith the mobile device.
 10. The system of claim 1, wherein the metadataindicates a geographic location associated with the respective geotaggedaudio signal, and weighting each geotagged audio signal comprisesweighting each geotagged audio signal based on a level of detaildefining the geographic location associated with the respectivegeotagged audio signal.
 11. The system of claim 1, wherein the metadataindicates a geographic location type associated with the respectivegeotagged audio signal, and weighting each geotagged audio signalcomprises weighting each geotagged audio signal based on the geographiclocation type associated with the respective geotagged audio signal. 12.The system of claim 1, wherein the metadata indicates a type of mobiledevice associated with the respective geotagged audio signal, andweighting each geotagged audio signal comprises weighting each geotaggedaudio signal based on the type of mobile device associated with thegeotagged audio signal.
 13. The system of claim 1, wherein the metadataindicates a time of day associated with the respective geotagged audiosignal, and weighting each geotagged audio signal comprises weightingeach geotagged audio signal based on the time of day associated with therespective geotagged audio signal.
 14. The system of claim 1, whereinthe metadata indicates a day of a week associated with the respectivegeotagged audio signal, and weighting each geotagged audio signalcomprises weighting each geotagged audio signal based on the day of theweek associated with the respective geotagged audio signal.
 15. Thesystem of claim 1, wherein weighting each geotagged audio signal furthercomprises weighting each geotagged audio signal after receiving theaudio signal that corresponds to the utterance.
 16. The system of claim1, wherein using the set of weighted geotagged audio signals to performnoise compensation comprises: using the set of weighted geotagged audiosignals to generate a noise model for the geographic location; andperforming noise compensation on the audio signal that corresponds tothe utterance using the generated noise model.
 17. The system of claim1, wherein the operations further comprise performing speech recognitionon the utterance using the noise-compensated audio signal.
 18. Thesystem of claim 1, wherein using the set of weighted geotagged audiosignals to perform noise compensation further comprises performing noisecompensation on the audio signal that corresponds to the utterance usingthe set of weighted geotagged audio signals and using an environmentalaudio portion of the audio signal that corresponds to the utterance. 19.A computer storage medium encoded with a computer program, the programcomprising instructions that when executed by one or more computerscause the one or more computers to perform operations comprising:receiving an audio signal that corresponds to an utterance recorded by amobile device; determining a geographic location associated with themobile device; identifying a set of geotagged audio signals thatcorrespond to environmental audio associated with the geographiclocation; weighting each geotagged audio signal of the set of geotaggedaudio signals based on metadata associated with the respective geotaggedaudio signal; and using the set of weighted geotagged audio signals toperform noise compensation on the audio signal that corresponds to theutterance.
 20. A computer-implemented method comprising: receiving anaudio signal that corresponds to an utterance recorded by a mobiledevice; determining a geographic location associated with the mobiledevice; identifying a set of geotagged audio signals that correspond toenvironmental audio associated with the geographic location; weightingeach geotagged audio signal of the set of geotagged audio signals basedon metadata associated with the respective geotagged audio signal; andusing the set of weighted geotagged audio signals to perform noisecompensation on the audio signal that corresponds to the utterance. 21.The computer-implemented method of claim 20, wherein the operationsfurther comprise receiving geotagged audio signals, each geotagged audiosignal including the metadata associated with the respective geotaggedaudio signal.
 22. The computer-implemented method of claim 20, whereinthe operations further comprise: receiving geotagged audio signals;generating the metadata for each geotagged audio signal; and associatingthe metadata with the respective geotagged audio signal.
 23. Thecomputer-implemented method of claim 20, wherein the metadata indicateswhether background voices are present in the respective geotagged audiosignal, and weighting each geotagged audio signal comprises weightingeach geotagged audio signal based on whether background voices arepresent in the respective geotagged audio signal.
 24. Thecomputer-implemented method of claim 20, wherein the metadata indicatesan accuracy of geographic location information associated with therespective geotagged audio signal, and weighting each geotagged audiosignal comprises weighting each geotagged audio signal based on theaccuracy of the geographic location information associated with therespective geotagged audio signal.
 25. The computer-implemented methodof claim 20, wherein the metadata indicates a length of the respectivegeotagged audio signal, and weighting each geotagged audio signalcomprises weighting each geotagged audio signal based on the length ofthe respective geotagged audio signal.
 26. The computer-implementedmethod of claim 20, wherein the metadata indicates a quality of therespective geotagged audio signal, and weighting each geotagged audiosignal comprises weighting each geotagged audio signal based on thequality of the respective geotagged audio signal.
 27. Thecomputer-implemented method of claim 20, wherein the metadata indicatesa geographic location associated with the respective geotagged audiosignal, and weighting each geotagged audio signal comprises weightingeach geotagged audio signal based on proximity of the geographiclocation associated with the respective geotagged audio signal to thegeographic location associated with the mobile device.
 28. Thecomputer-implemented method of claim 20, wherein the metadata indicatesa geographic location associated with the respective geotagged audiosignal, and weighting each geotagged audio signal comprises weightingeach geotagged audio signal based on a level of detail defining thegeographic location associated with the respective geotagged audiosignal.
 29. The computer-implemented method of claim 20, wherein themetadata indicates a geographic location type associated with therespective geotagged audio signal, and weighting each geotagged audiosignal comprises weighting each geotagged audio signal based on thegeographic location type associated with the respective geotagged audiosignal.
 30. The computer-implemented method of claim 20, wherein themetadata indicates a type of mobile device associated with therespective geotagged audio signal, and weighting each geotagged audiosignal comprises weighting each geotagged audio signal based on the typeof mobile device associated with the geotagged audio signal.